1. Field of the Invention
The present invention relates to directional input devices particularly for use in portable electronic devices.
2. Background Art
Highly portable electronic devices, such as personal digital assistants, portable telephones, remote controls, and the like, provide increasing functionality to their users. This functionality often accompanies an increased need for information from the user. To fulfill this need, portable electronic devices incorporate mouse pointing sensors that provide directional input using a single finger, often from the same hand that holds the electronic device. In addition, many such mouse pointing sensors provide a magnitude signal in relation to force supplied by the user. This force may be applied through a joystick or a mouse button. Signals generated by such mouse pointing sensors are conditioned and processed by on-board logic to activate a pointer displayed on a graphical user interface either incorporated into the hand-held device or separated from the handheld device, such as with a television remote control.
New portable electronic devices must be light, reliable, and inexpensive. This latter requirement dictates a mouse pointing sensor which is both inexpensive and easily manufacturable into the handheld device. In addition, the mouse pointing sensor must be small. The sensor must not require a large footprint on a handheld device printed circuit board. In addition, the sensor must not require significant vertical distance away from the printed circuit board.
One type of sensor used in portable electronic devices operates with a strain gauge stick. Moving the stick creates strain induced changes in resistance. One difficulty with such devices is that the strain induced resistance change creates a small signal, requiring amplification and introducing noise susceptibility. In addition, these devices have a flex circuit tail which requires a connector on the printed circuit board. The sensor is often mechanically mounted to the printed circuit board with screws. Thus, both the device and its manufacture into a portable electronic system is expensive.
Another sensor type is the Force Sensing Resistor™ (FSR). Various FSRs have been disclosed, such as those described in commonly assigned U.S. Pat. Nos. 4,314,227 and 4,314,228, each of which is hereby incorporated by reference in its entirety. Typically, an FSR is composed of three parts: a rigid base, a spacer, and a resistive membrane. The flexible resistive membrane is spaced apart from the base layer by a spacer, which is typically a ring of material around the outer edge of the conductive traces. The spacer is also typically coated with adhesive to hold the device together. The flexible top membrane may be made of a polymer coated on its inner face with semi-conductive or resistive ink, giving the FSR force sensing properties. This ink is described in commonly owned U.S. Pat. Nos. 5,296,837 and 5,302,936, each of which is hereby incorporated by reference in its entirety.
Conductive traces within the FSR are typically arranged in separated interdigitated sets on the base. These traces may be configured in a single zone or, more relevant to the present invention, in multiple zones allowing pointing devices as described in commonly assigned U.S. Pat. No. 5,659,334, which is hereby incorporated by reference in its entirety.
For use in portable electronic devices, the FSR must be connected to sensing and conditioning electronics. One way this may be accomplished is by connecting the FSR to a printed circuit board through a multi-conductor cable. Another way of connecting the FSR to support electronics is to adhere the FSR base directly to a printed circuit board containing the electronics through z-tape. Z-tape is adhesive on both sides and conducts electricity in a direction perpendicular to the tape surface. While either of these methods is effective, both have manufacturing steps and components which are necessary only for mounting purposes. If these components and their associated manufacturing steps could be eliminated, the cost of any system containing such an FSR could be reduced. In addition, the reliability of such a system would be increased.
What is needed is a mouse pointing transducer and a method of manufacturing such a transducer into a portable electronic device that eliminates unnecessary components and requires fewer manufacturing steps without sacrificing transducer performance.